This invention relates to disc valves and more particularly to improved disc valves which effect stoppage of liquid flow in response to slight back pressures against the valve.
There are many occasions where is it desirable to have two or more sources of liquid flow sequentially through a common feed line without the need for an operator to be present to manipulate controls so that liquid from secondary sources will flow through the common line when liquid from a primary source has been depleted. This is desirable particularly in the medical field when parenteral solutions are being administered to patients. On occasions, while a primary solution is being administered it is necessary to give an additive solution without its being diluted by the primary solution. If the volume of the additive solution is small, it can be introduced rapidly under pressure by hypodermic syringe through a medicinal entry or injection bulb included in the set for that purpose. An administration set such as that disclosed in U.S. Pat. No. 2,999,499 shows how this can be accomplished. When an additive solution is injected, check valve 22 serving as the medicinal entry, the considerable pressure exerted causes the disc in disc valve 9 to close the inlet from the primary solution so that the additive enters the patient's vein undiluted. However, when larger volumes of an additive or a secondary solution are to be administered, particularly over a prolonged period of time, such an arrangement is not workable since the secondary solution is introduced under considerably less pressure, a pressure generally insufficient to close off the disc valve in the primary line.
In U.S. Pat. No. 3,886,937 there is disclosed an administration set which is adapted for the introduction of a secondary solution under low pressures over prolonged periods without the need for manipulation by an attendent. This procedure is accomplished by means of a duck bill check valve in the primary line which is normally closed but which will open to the flow of liquid from a primary source by gravity and close if a secondary solution is introduced in the line below the valve which has a head pressure greater than the head pressure of the primary source by at least one inch of water. Although this type of check valve has considerable merit for such use in administration of additive solutions, it has certain drawbacks. The chief problem is that in the manufacture of the resilient duck bill member, the lips do not always come together in a closed manner and often leave an opening between them which is difficult to detect. This results in an incompetant valve which may not close with a very small back pressure exerted by the secondary solution. Particulates can also become lodged between the lips of the valve and prevent closure.